1. Field of the Invention
This invention relates to homogeneous, liquid conditioners for softening fabrics stiffened by washing in hard water, and a process for their manufacture.
2. Statement of the Related Art
In areas where the water is particularly hard, the underdosage of detergents in the washing of fabrics or the use of unsuitable detergents is known to produce deposits of dissolved minerals, especially lime, both on fabrics and also in the washing machines used. Under these conditions, the washed fabrics soon become gray and patchy and feel unpleasantly stiff. In order to overcome these disadvantages and to soften (delime) the stiffened fabrics, the fabrics are treated after washing in a rinsing cycle, for example with urea adducts of nitric acid or phosphoric acid, with amido-sulfonic acid, or with other acids. Unfortunately, this can give rise to extremely serious corrosion of the brass or copper parts of washing machines.
In German patent application No. 14 94 847, it is proposed to improve powdered, storable deliming preparations based on an adduct of urea and phosphoric acid by adding to them from 3 to 60% by weight of maleic acid anhydride. More rapid and complete dissolution of the incrustations, which normally consist of lime and rust, is said to be obtained in this way. From 0.1 to 3% by weight of cationic, anionic or nonionic surfactants may also be added to the preparations in question to improve their wetting power. The inclusion of corrosion inhibitors is also recommended although, in contrast to known acidic deliming preparations, the preparations in question have only a very slight corrosive effect and are stated to be kind to fibers. According to Example 1, 2% of coconut oil fatty alcohol sulfate was dissolved in a mixture of 40% by weight of (100%) phosphoric acid and 8% by weight of water and 10% by weight of powder-form maleic acid anhydride was added to the resulting solution. 27% by weight of urea was then added. After cooling and solidification of the mixture, 11% by weight of anhydrous sodium sulfate and 2% by weight of finely divided silica were added to improve the properties of the powder.
It has been found that the production of these effective deliming preparations on an industrial scale is too complicated and, therefore, too cost intensive. The production can only be carried out in factories equipped with the latest machinery, which unfortunately are not available to the required extent. In addition, consumers prefer liquid deliming preparations because they are easier to use in measured quantities.
Accordingly, it was obvious to try to overcome the inadequacies of the prior art by manufacturing and marketing the ingredients known from German patent application No. 14 94 847 in the form of aqueous solutions without the adsorbents, (sodium sulfate and finely divided silica), which are not required for liquid products. Unfortunately, this attempt resulted in an aqueous solution with a crystalline sediment for otherwise the same concentrations of the ingredients. Although a reduction in the phosphoric acid content to 40% by weight without any change in the concentrations of the other ingredients produced a clear solution, this clear solution separated into two phases and, on further reduction of the phosphoric acid content to 38% by weight, also became cloudy.
The replacement of maleic acid anhydride by pure maleic acid and of the anionic surfactant by 2 or 3% by weight of a nonyl phenol reacted with 10 moles of ethylene oxide initially resulted in clear solutions which were still stable after 2 days, even at room temperature, but which became solid and cloudy and could not be reliquefied after 24 hours in an alternating climate cell (-10.degree. C./+40.degree. C.).
Accordingly, it was found that the teachings of the prior art, which applied to a homogeneous powdered product, could not be readily applied to the required liquid products. The problem was solved by reformulating the compositions.